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I'm on tour in Australia...

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Some of them might recollapse
in a fraction of a second.

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Others might be blown apart
by loads of dark energy.

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...talking about
the life of our universe

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to scientists
and to space-loving audiences.

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I just like having
my brain stretched.

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I'll probably just stop and have
a look at the stars on the way home.

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On our journey so far, we've explored
how our universe began.

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So, this is the oldest light
in the universe.

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But what about our future?

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Is there an end of the universe?
Is our universe eternal?

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The universe literally
tears itself apart.

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There is some true vacuum somewhere.

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We could tunnel into it
at any moment.

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Does it make any sense
to talk about this universe

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in 100 billion, 200 billion,
a trillion years' time?

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Will there be stars and galaxies?

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And people, and questions,

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and astronomers, and televisions?

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What IS the fate of the universe?
How will it all end?

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I suppose we all get used to the idea
that we live finite lives,

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and perhaps that's 'cause we imagine
we can leave a legacy -

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our children and grandchildren,
great works.

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But will that legacy be eternal?

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Can we imagine taking the great
achievements of our civilisation

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and chiselling them into granite
and leaving them

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as a record into the far future?

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Or do the laws of nature conspire
to make that impossible?

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Will all trace of our civilisation
one day vanish?

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What will be our fate?

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And what is the ultimate fate
of the universe?

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I'm going to investigate the theories
that cosmologists have put forward

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for the end of days.

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There is a law of physics

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called the second law
of thermodynamics,

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and to paraphrase it,
it means that on a global scale -

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so, across the universe -

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things can only get worse.

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So, things tend to get
more disordered,

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things tend to decay away.

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I was once involved in putting
forward the opposite proposition -

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things can only get better -

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but that is a gross violation
of the second law of thermodynamics.

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It really shouldn't have been allowed
even in a song lyric.

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♪ Things

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♪ Can only get better... ♪

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I think, actually,

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songwriters should pay more attention
to fundamental physics.

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The first stars in our universe
began to shine

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around 100 million years
after the big bang.

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But it was another 9 billion years
before our star, the sun, formed.

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But our sun won't live forever,

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which will obviously have a direct
impact on all life on Earth.

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The sun is about halfway through the
phase where it's burning hydrogen.

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It's making helium.

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It's got what we call
the 'solar luminosity' -

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it's putting out
that much heat and light.

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But that is going to be
slowly increasing.

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Presumably at some point we would
find it extremely uncomfortable here.

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Yeah.

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In about 1.1 billion years,

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it will have got to 10% brighter
than it is now.

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That is enough to create
what's called a moist greenhouse.

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So life on Earth will become
very problematic at that stage.

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3.5 billion years from now,

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it'll be 1.4 times
its current luminosity,

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and that's enough
to evaporate the oceans.

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Right.

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So that's getting fairly severe
at that stage.

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It's really got
another 5 billion years to go

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that it can keep on
burning hydrogen,

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but it will become uncomfortable
for us well before that.

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The destiny of stars like our sun
is to run out of fuel and collapse.

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The core compresses, but the rest
of the star expands enormously

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and we have a red giant.

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So we enter this red giant phase.

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When our sun becomes a red giant

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and it begins to swell and engulf
the orbit of Mercury,

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it's gonna start getting
very hot on Earth.

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We're gonna need ways
to terraform Mars

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and then ship billions of people
to Mars,

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because Mars will be cooler
than Earth,

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it being one and a half times
farther away.

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The Earth will basically get fried
at that point.

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We won't be able to exist.

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Hopefully, if humans are still
around in some form or another,

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we've moved off to better locales.

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So, the ultimate fate of our star,
the sun, is to be this cooling ember?

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That's the ultimate fate of the sun.

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So, in just over a billion years,
this place will become uninhabitable.

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In 6 to 7 billion years,
the sun will be gone.

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But that, of course,
isn't the end for the universe,

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and matter that floats out
from our dying sun

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will recollapse to other stars,
other planets

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and perhaps other living things.

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But that process can't go on forever.

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There comes a point
in the life of the universe

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when the constant recycling,
the births of new stars, has to stop.

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So, what IS the fate of the universe?

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How will it all end?

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Cosmologists have thought about this
for a long time,

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and many have come to the conclusion
that the end will come

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in more of a whimper than a bang.

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It's known as the heat death,

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and it begins with a decrease
in the rate of star formation.

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Looking up into the southern sky

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allows us to see a hint
of this process.

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As soon as you look
through a telescope,

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you do get a sense of the amount of
gas and stuff out there, don't you?

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You always hear this wonderful phrase
'stellar nurseries'.

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So, is that really accurate,

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that you really do have these places
where all the action is concentrated?

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Absolutely.

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In order to form stars, you have
to put together a lot of material,

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and so you naturally pop off a lot
of stars in that particular area.

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I can't...
I can't stop looking, actually.

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Fortunately, we have
very powerful telescopes

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to see all the way across the galaxy

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so that we can pick out stars

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in all kinds of stages
of their formation process,

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from when they just start collapsing

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to when they really kick on
and turn into full-blown stars.

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Stars form from collapsing clouds
of gas and dust.

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And the leftover material
forms into planets and moons

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and asteroids and comets.

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But in our part of the Milky Way,

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this construction process
is slowing down.

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Is this a glimpse
of the beginning of the end?

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We see that around
the, sort of, solar neighbourhood,

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around where the sun lives,

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that there's about half as much
star formation

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as there was 10 billion years ago.

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Why is that?

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Once you form a star, it dies

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and it holds
some of its matter together

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in a black hole or a white dwarf
or a neutron star,

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and you've locked that gas up
forever

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and it never goes back
to being a star again.

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So in order to keep forming stars,

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you've got to keep bringing gas in
from somewhere else.

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So the fact that
the rate is dropping...

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...you said a factor of two from,
what, 10 billion years ago to now,

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implies, of course, that some time
in the future, that's gonna stop.

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So, when is that?

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It's a long time.
Not in our lifetimes.

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I think if you do the extrapolation,

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you go out 100 billion years
or something, more than that.

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It's a long time away.

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Eventually, we will run out of gas
to form new stars

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in every single galaxy,

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and gradually, gradually, gradually,
the universe will... die away.

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So, what will our descendants
actually see

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when they look up into the night sky
in a few billion years' time?

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Well, the centre of the galaxy
is here, isn't it?

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Yeah. It's kind of the empty bit
of sky up here - Sagittarius.

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Peer into the centre of the Milky Way

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and, like virtually
all other galaxies,

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you'll find
a supermassive black hole.

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Ours is around 4 million times
the mass of the sun.

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We don't know how these
supermassive black holes form,

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but we do know about smaller,
stellar-mass black holes.

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And when the centre of those stars
are more massive

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than about two or three times
the mass of our sun,

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they actually collapse
into a singularity,

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is the theory,

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and the space-time around them
bends completely on itself,

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so nothing...

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The gravitational pull is so strong,
nothing, even light, can't escape.

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So, then we're left, I suppose,
with a dark sky,

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but a sky full of black holes...

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Yeah.
..and, what, fading stellar remnants?

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Yeah, fading stellar remnants.

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Things like faintly glowing cores
of long dead stars,

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billions or even trillions of years
in the future,

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and these are glowing so faintly,
you can't even see them.

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Now, black holes do radiate
very, very faintly,

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but we won't actually be able
to see that,

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because they'll all be
too far apart.

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You get the sense, I suppose,
when you talk about that,

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this starry sky, we take for granted.

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Although, perhaps we don't.

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You know, perhaps
it's the most beautiful thing

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but it's a temporary phenomenon.

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It's actually a very short-term
phenomenon, isn't it?

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We're only nearly 14 billion years
into the universe's history.

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So in the far, far future,
hundreds of billions of years' time,

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if we could still stand somewhere
and look out into the night sky,

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we would see just blackness,

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and there would be no hints at all
to tell us

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about the past glorious history
of our universe.

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But is this the whole picture?

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Science has a habit of
opening up new possibilities -

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often when you least expect them.

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00:12:09,657 --> 00:12:13,416
We've known our universe is expanding
since the 1920s,

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and we thought the expansion rate
was slowing down.

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Then, in the late 1990s,
it was discovered

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that the expansion rate of our
universe is actually speeding up.

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00:12:26,217 --> 00:12:28,456
Nobel Prize winner Brian Schmidt

199
00:12:28,457 --> 00:12:31,297
was as surprised as anyone
by his discovery.

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1998,
we went through and we measured

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that the universe wasn't slowing
down at all - it was speeding up.

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And that was... well,
it looked to me like a big mistake

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and that I had somehow wasted
three and a half years of my life

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getting some nonsensical answer.

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We knew that Einstein
had invented something -

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called 'dark energy'
or the 'cosmological constant',

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00:12:55,177 --> 00:12:57,656
which makes gravity push
rather than pull,

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00:12:57,657 --> 00:12:59,216
but that seemed pretty crazy -

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that was, sort of,
Einstein's 'bad idea'.

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If the universe continues
to expand forever

211
00:13:10,377 --> 00:13:13,616
and indeed continues to accelerate
in its expansion,

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then in the far future,

213
00:13:15,537 --> 00:13:18,856
you end up with a universe
that's just a sea of photons

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00:13:18,857 --> 00:13:21,896
being stretched
by the expansion of space

215
00:13:21,897 --> 00:13:24,416
and cooling down
to the same temperature,

216
00:13:24,417 --> 00:13:27,456
so you end up with a universe
where there is no structure.

217
00:13:27,457 --> 00:13:31,416
There's no possibility
of storing any information

218
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or processing any information,

219
00:13:33,297 --> 00:13:36,496
no possibility of consciousness
or life,

220
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no structures at all,

221
00:13:38,577 --> 00:13:43,497
and that sea of cooling photons
will last forever.

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00:13:47,737 --> 00:13:51,376
The idea that there is a mysterious
thing called 'dark energy'

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which drives the accelerating
expansion of our universe forever

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is the standard model of cosmology.

225
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But it's not the only theory
about how our universe could end.

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00:14:07,977 --> 00:14:09,336
The 'heat death' -

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this idea the universe
just gradually grinds to a halt

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and carries on expanding forever -

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is a bit miserable,

230
00:14:17,937 --> 00:14:24,176
but the physics of the far future
is not very well understood.

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00:14:24,177 --> 00:14:29,137
So there are, in fact, other, and I
think more exciting, possibilities.

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00:14:32,457 --> 00:14:34,376
So, like the Robert Frost poem,

233
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it seems like things will end
in ice, not in fire.

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But there's a big caution here,

235
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which is we don't really understand
dark energy very well,

236
00:14:41,657 --> 00:14:46,416
and so this is really only one
of a couple of possibilities.

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00:14:46,417 --> 00:14:50,576
Cosmologists have come up with
an even more devastating idea

238
00:14:50,577 --> 00:14:53,456
called 'phantom dark energy',

239
00:14:53,457 --> 00:14:58,057
which eventually leads to
the universe ripping itself apart.

240
00:15:01,577 --> 00:15:04,176
If the universe has
this dark energy,

241
00:15:04,177 --> 00:15:07,897
this stuff causes gravity
to push from itself.

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00:15:08,977 --> 00:15:12,137
This is another really great way
to destroy the universe.

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00:15:13,457 --> 00:15:15,536
So as the universe gets bigger,

244
00:15:15,537 --> 00:15:18,296
this stuff dominates the universe
more and more,

245
00:15:18,297 --> 00:15:19,976
because it's part of space itself.

246
00:15:19,977 --> 00:15:22,976
You make more space,
you have more dark energy,

247
00:15:22,977 --> 00:15:26,257
which makes dark energy stronger
over the other forms of gravity.

248
00:15:28,217 --> 00:15:31,656
Over time, this phantom dark energy

249
00:15:31,657 --> 00:15:34,576
would start to pull apart
bound orbits.

250
00:15:34,577 --> 00:15:36,536
So, first, it would pull apart
the galaxy.

251
00:15:36,537 --> 00:15:40,096
Stars would start to wander off,
'cause it's still increasing.

252
00:15:40,097 --> 00:15:44,296
It'll start to break up
all structure, all matter.

253
00:15:44,297 --> 00:15:45,656
And then at some point,

254
00:15:45,657 --> 00:15:50,496
the entire universe will be...
torn asunder, in some sense.

255
00:15:50,497 --> 00:15:51,857
It's called the 'big rip'.

256
00:15:55,137 --> 00:15:57,576
You reach the...
the breaking point, literally,

257
00:15:57,577 --> 00:16:00,136
and the fabric of the universe
starts to tear a hole,

258
00:16:00,137 --> 00:16:02,896
the laws of the universe
and the boundaries of the universe

259
00:16:02,897 --> 00:16:04,136
just start going haywire.

260
00:16:04,137 --> 00:16:06,016
So that's the big rip?
So that's the big rip.

261
00:16:06,017 --> 00:16:07,816
I mean, that's one of
the theories, right?

262
00:16:07,817 --> 00:16:09,456
There's the big rip
and the big freeze.

263
00:16:09,457 --> 00:16:11,376
I love the big rip, 'cause...

264
00:16:11,377 --> 00:16:13,377
...who doesn't like
a universe ripping, right?

265
00:16:16,577 --> 00:16:20,376
The 'big rip' idea can be combined
with a theory we have

266
00:16:20,377 --> 00:16:24,536
describing the beginning of
our universe, known as inflation,

267
00:16:24,537 --> 00:16:27,856
which describes a time
before the hot big bang,

268
00:16:27,857 --> 00:16:31,497
when our universe was expanding
extremely rapidly.

269
00:16:35,457 --> 00:16:37,336
So, inflation...
That's right.

270
00:16:37,337 --> 00:16:39,536
...that rapid expansion
before the big bang,

271
00:16:39,537 --> 00:16:42,976
could be envisaged as being the end
of a previous universe

272
00:16:42,977 --> 00:16:44,656
that's undergoing a big rip?

273
00:16:44,657 --> 00:16:47,176
Exactly. It's... you know,
you have these big questions,

274
00:16:47,177 --> 00:16:48,816
but when you look at it
fundamentally,

275
00:16:48,817 --> 00:16:51,296
if you have a universe that grows
quickly through dark energy,

276
00:16:51,297 --> 00:16:52,576
which rips,

277
00:16:52,577 --> 00:16:55,976
that would mimic pretty similar to
what we think happened in inflation.

278
00:16:55,977 --> 00:16:59,856
We are pretty confident we know
inflation had to happen in some form

279
00:16:59,857 --> 00:17:01,376
to get the universe
that we see today,

280
00:17:01,377 --> 00:17:04,736
so it's not crazy to think
that these two things are related.

281
00:17:04,737 --> 00:17:06,576
We don't have
the evidence for it yet,

282
00:17:06,577 --> 00:17:09,257
but it's not the worst idea
we've had.

283
00:17:13,377 --> 00:17:16,976
We said that inflation stops
and the big bang happens.

284
00:17:16,977 --> 00:17:20,936
But what if inflation
doesn't stop all at once -

285
00:17:20,937 --> 00:17:22,816
it just stops in patches?

286
00:17:22,817 --> 00:17:27,656
So then our big bang
would just be a little event

287
00:17:27,657 --> 00:17:30,016
in an ever inflating space.

288
00:17:30,017 --> 00:17:33,696
And there'll be other patches
that stop and you get a universe,

289
00:17:33,697 --> 00:17:36,696
other patches that stop
and you get a universe.

290
00:17:36,697 --> 00:17:41,296
And that process could go on forever.

291
00:17:41,297 --> 00:17:44,696
So, although our universe dies,

292
00:17:44,697 --> 00:17:47,976
other universes
are constantly being created.

293
00:17:47,977 --> 00:17:51,217
This is called
the inflationary multiverse.

294
00:18:01,217 --> 00:18:03,176
So you get
this wonderful process

295
00:18:03,177 --> 00:18:06,256
of big bang after big bang
after big bang,

296
00:18:06,257 --> 00:18:09,217
yielding universe
after universe after universe.

297
00:18:12,097 --> 00:18:13,576
How are we to picture that?

298
00:18:13,577 --> 00:18:17,216
Are we to picture our universe
riding on the back

299
00:18:17,217 --> 00:18:21,136
of some kind of... potentiality
of expanding space-time?

300
00:18:21,137 --> 00:18:22,456
You can.

301
00:18:22,457 --> 00:18:24,216
I've got a more down-to-earth way,
which is,

302
00:18:24,217 --> 00:18:26,056
think of a big piece
of Swiss cheese,

303
00:18:26,057 --> 00:18:28,016
big block of Swiss cheese, right?

304
00:18:28,017 --> 00:18:31,096
Each of the openings
is like a universe,

305
00:18:31,097 --> 00:18:34,176
and the cheese itself
is the inflaton field

306
00:18:34,177 --> 00:18:38,176
driving the ever accelerated
expansion of the universe.

307
00:18:38,177 --> 00:18:40,536
And as this cheese expands,

308
00:18:40,537 --> 00:18:43,016
more and more pockets
open up inside -

309
00:18:43,017 --> 00:18:45,176
more and more universes are created.

310
00:18:45,177 --> 00:18:47,816
And our universe
is simply one opening

311
00:18:47,817 --> 00:18:49,176
in the block of Swiss cheese -

312
00:18:49,177 --> 00:18:50,497
that's all that we are.

313
00:19:00,137 --> 00:19:02,776
The idea of a multiverse is tricky
to get your head around.

314
00:19:02,777 --> 00:19:06,297
This is where we keep...
the cream of the crop.

315
00:19:07,457 --> 00:19:10,256
But I'm hoping
a glass of Aussie shiraz

316
00:19:10,257 --> 00:19:12,616
will enhance my powers of analogy.

317
00:19:12,617 --> 00:19:14,936
Cheers. Thank you.

318
00:19:14,937 --> 00:19:18,256
I'm tempted to draw the analogy
with inflationary cosmology...

319
00:19:18,257 --> 00:19:19,576
Well, of course.

320
00:19:19,577 --> 00:19:21,976
...and say that each one of these
is like a different universe

321
00:19:21,977 --> 00:19:23,616
with different physical laws.

322
00:19:23,617 --> 00:19:26,336
Each barrel in this warehouse

323
00:19:26,337 --> 00:19:28,216
is taken from a different part
of the vineyard,

324
00:19:28,217 --> 00:19:31,536
so each barrel is a different
expression through the grapes

325
00:19:31,537 --> 00:19:33,016
of the landscape.

326
00:19:33,017 --> 00:19:35,176
So, in that analogy,

327
00:19:35,177 --> 00:19:38,296
our universe would be
just one barrel -

328
00:19:38,297 --> 00:19:41,376
of shiraz viognier, in this case -

329
00:19:41,377 --> 00:19:45,376
amongst a whole possible warehouse
of barrels,

330
00:19:45,377 --> 00:19:48,416
different expressions
of possibilities.

331
00:19:48,417 --> 00:19:51,177
It's a good analogy.
It's not too forced.

332
00:19:55,617 --> 00:20:00,536
Physicists refer to each different
possibility as a different vacuum,

333
00:20:00,537 --> 00:20:05,097
and this opens up the chance that
we could be instantly annihilated.

334
00:20:08,297 --> 00:20:11,016
My favourite way to destroy
the universe is vacuum decay,

335
00:20:11,017 --> 00:20:12,976
which is a really fun idea

336
00:20:12,977 --> 00:20:15,616
and... and one that's gotten
really popular lately

337
00:20:15,617 --> 00:20:18,897
because of things that we're seeing
at the Large Hadron Collider.

338
00:20:22,337 --> 00:20:26,336
The Large Hadron Collider at CERN,
on the French-Swiss border,

339
00:20:26,337 --> 00:20:28,977
is the largest scientific machine
in the world.

340
00:20:34,857 --> 00:20:38,537
In 2012, the Higgs boson
was discovered here.

341
00:20:40,457 --> 00:20:42,576
But its properties suggest

342
00:20:42,577 --> 00:20:46,777
that our universe could be in
an unstable 'false vacuum' state.

343
00:20:49,977 --> 00:20:52,616
There is some true vacuum somewhere,

344
00:20:52,617 --> 00:20:57,336
and we could... maybe tunnel into it
at any moment...

345
00:20:57,337 --> 00:20:59,416
...you know,
and just destroy the universe.

346
00:20:59,417 --> 00:21:02,256
By any moment, you probably...
I mean, it's unlikely.

347
00:21:02,257 --> 00:21:03,856
You're a cosmologist.

348
00:21:03,857 --> 00:21:06,617
If you're still watching this,
it hasn't happened yet.

349
00:21:09,137 --> 00:21:13,696
The timescale for vacuum decay is
many times the age of our universe,

350
00:21:13,697 --> 00:21:15,736
so it's not gonna happen tomorrow.

351
00:21:15,737 --> 00:21:18,856
But it's still disconcerting
to think that our universe

352
00:21:18,857 --> 00:21:23,577
ISN'T the stable, eternal home
we once believed it to be.

353
00:21:26,177 --> 00:21:30,496
But you might think, "Well,
quantum mechanics, could it save us?"

354
00:21:30,497 --> 00:21:34,696
"Could there be a little fluctuation
that allows something to happen"

355
00:21:34,697 --> 00:21:38,616
"and reboot
part or all of the universe?"

356
00:21:38,617 --> 00:21:40,417
You know, you never know.

357
00:21:41,617 --> 00:21:42,937
But probably not.

358
00:21:47,977 --> 00:21:50,536
Whether it's vacuum decay, a big rip

359
00:21:50,537 --> 00:21:55,936
or a sad, slow heat death over
the next 10 to the 1,000 years,

360
00:21:55,937 --> 00:22:00,096
now is the time
to explore our universe,

361
00:22:00,097 --> 00:22:01,537
while it's still visible to us.

362
00:22:04,857 --> 00:22:08,136
We live in a special time
in the universe's history -

363
00:22:08,137 --> 00:22:11,496
the time when the universe
is young enough

364
00:22:11,497 --> 00:22:15,816
that we can look out into the night
sky and see billions of galaxies.

365
00:22:15,817 --> 00:22:19,656
The galaxies are not receding
away from us fast enough

366
00:22:19,657 --> 00:22:21,737
that they outrun the light.

367
00:22:29,857 --> 00:22:32,576
So, our descendants,
when they look out into deep space,

368
00:22:32,577 --> 00:22:36,336
will see black, inky,
dark stillness.

369
00:22:36,337 --> 00:22:39,056
And they'll think that this little
collection of galaxies

370
00:22:39,057 --> 00:22:41,816
that are all bound together
gravitationally nearby,

371
00:22:41,817 --> 00:22:43,416
they'll think that's it.

372
00:22:43,417 --> 00:22:45,336
And that's a wrong picture
of the universe,

373
00:22:45,337 --> 00:22:47,576
but nevertheless, that's the picture
which our descendants

374
00:22:47,577 --> 00:22:50,336
are gonna naturally be led to
through their own observations.

375
00:22:50,337 --> 00:22:54,016
The future astronomers
in 2 and 4 and 6 billion years

376
00:22:54,017 --> 00:22:57,136
will think we're crazy, 'cause they
can't see the evidence that we have.

377
00:22:57,137 --> 00:22:59,456
I think, actually, it was
Brian Greene who said to us

378
00:22:59,457 --> 00:23:02,936
that cosmology essentially
becomes a religion.

379
00:23:02,937 --> 00:23:04,096
That's right, yeah.

380
00:23:04,097 --> 00:23:05,896
'Cause all you've got is
history books telling you...

381
00:23:05,897 --> 00:23:07,016
Exactly.

382
00:23:07,017 --> 00:23:08,456
...about the oldest light
in the universe.

383
00:23:08,457 --> 00:23:10,816
That's right. You can't go
and reproduce the experiment.

384
00:23:10,817 --> 00:23:12,696
We would just have to believe
someone else's word.

385
00:23:12,697 --> 00:23:14,176
And then... what are we doing?

386
00:23:14,177 --> 00:23:17,976
Who are we to think,
who are we to say

387
00:23:17,977 --> 00:23:22,016
that WE have a complete record
of the universe to draw from?

388
00:23:22,017 --> 00:23:25,696
What chapters of
our book of the universe

389
00:23:25,697 --> 00:23:28,617
had been removed before
we even acquired the book?

390
00:23:32,497 --> 00:23:35,856
The fascinating thing
about the far future

391
00:23:35,857 --> 00:23:38,616
in an accelerating
and expanding universe

392
00:23:38,617 --> 00:23:43,096
is that you get to a point where
you can't do cosmology anymore -

393
00:23:43,097 --> 00:23:45,296
there's no such science as cosmology.

394
00:23:45,297 --> 00:23:48,376
You couldn't deduce from what you see

395
00:23:48,377 --> 00:23:50,656
that you live in
an expanding universe

396
00:23:50,657 --> 00:23:53,216
that had an origin
at some point in the past.

397
00:23:53,217 --> 00:23:56,536
So cosmology becomes a subject

398
00:23:56,537 --> 00:23:59,696
that is only accessible
through ancient books

399
00:23:59,697 --> 00:24:02,336
and not accessible through
the things you can see.

400
00:24:02,337 --> 00:24:06,976
So, in that sense, I think that
the future of the universe is sad,

401
00:24:06,977 --> 00:24:09,696
because your ability
to gather knowledge

402
00:24:09,697 --> 00:24:11,896
about the universe
as it was in its past

403
00:24:11,897 --> 00:24:13,497
disappears.

404
00:24:17,097 --> 00:24:19,017
How will the universe end?

405
00:24:20,737 --> 00:24:22,416
I have no idea.

406
00:24:22,417 --> 00:24:23,776
I don't know.

407
00:24:23,777 --> 00:24:25,376
I don't know.

408
00:24:25,377 --> 00:24:27,176
You know, it's very difficult
to make predictions

409
00:24:27,177 --> 00:24:28,536
about the fate of the universe

410
00:24:28,537 --> 00:24:30,816
when there's 95%
we don't understand.

411
00:24:30,817 --> 00:24:32,416
OK.

412
00:24:32,417 --> 00:24:35,136
We should just make a documentary
called I Don't Know.

413
00:24:35,137 --> 00:24:37,496
Galaxies are forming
and stars are exploding

414
00:24:37,497 --> 00:24:41,016
and, you know, we're seeing evidence
of things happening in the big bang

415
00:24:41,017 --> 00:24:43,816
and the universe is expanding
ever faster,

416
00:24:43,817 --> 00:24:46,056
and we're just sitting here
drinking our tea.

417
00:24:46,057 --> 00:24:47,497
Yeah.
You know?

418
00:24:53,097 --> 00:24:54,776
I've had the good fortune

419
00:24:54,777 --> 00:24:58,056
to share my enthusiasm
for physics and the cosmos

420
00:24:58,057 --> 00:25:01,416
with Australian audiences
curious to contemplate

421
00:25:01,417 --> 00:25:03,376
the nature of our universe.

422
00:25:03,377 --> 00:25:05,496
Amazing.
Absolutely tremendous. Yeah.

423
00:25:05,497 --> 00:25:07,656
Oh, he takes us on
a great journey, I think.

424
00:25:07,657 --> 00:25:09,336
Did you understand it all?

425
00:25:09,337 --> 00:25:12,736
Uh... not all of it, but, yeah,
bits and pieces of it, yes.

426
00:25:12,737 --> 00:25:15,616
I love the fact that when I finish
work after a really hard day,

427
00:25:15,617 --> 00:25:17,136
I can come to something like this

428
00:25:17,137 --> 00:25:18,896
and he can make me feel
really insignificant

429
00:25:18,897 --> 00:25:21,417
compared to the rest
of the universe.

430
00:25:23,577 --> 00:25:28,976
And I've met scientists under
a truly inspiring southern night sky

431
00:25:28,977 --> 00:25:32,976
who share that curiosity
and desire to know more.

432
00:25:32,977 --> 00:25:35,217
We've got work to do!

433
00:25:36,537 --> 00:25:37,896
I suppose there are two ways

434
00:25:37,897 --> 00:25:39,976
of looking at the future
of the universe.

435
00:25:39,977 --> 00:25:42,296
You might feel depressed

436
00:25:42,297 --> 00:25:46,576
that although the universe will
almost certainly exist forever,

437
00:25:46,577 --> 00:25:49,056
we certainly won't.

438
00:25:49,057 --> 00:25:51,096
There will come a time in the future

439
00:25:51,097 --> 00:25:54,776
when it's not possible
for ANY life to exist.

440
00:25:54,777 --> 00:25:57,376
Or you might feel fortunate.

441
00:25:57,377 --> 00:25:59,856
You might feel fortunate
that we live in a time

442
00:25:59,857 --> 00:26:02,136
when we can look out
into the night sky

443
00:26:02,137 --> 00:26:06,016
and see the light from
distant stars and galaxies

444
00:26:06,017 --> 00:26:10,336
and from the very origin
of time itself

445
00:26:10,337 --> 00:26:14,696
and understand how our universe began

446
00:26:14,697 --> 00:26:17,977
and make predictions
about how it might end.

447
00:26:34,497 --> 00:26:37,096
Captions by Ericsson Access Services

448
00:26:37,097 --> 00:26:39,816
Copyright Australian
Broadcasting Corporation